So in this example, the customer could opt for Priority Mail International for $65 bringing the total to $255. I have no idea what the total customs fees would be. Let's use 30% or approximately $75 bringing the grand total to $330. (If anyone has actual customs fee info for South Africa on imported ant farm supplies, please provide it here.)
Based on Serafine's suggested pricing, the alternative would be 1/3 the price or about $100 -- a difference of $230. So the decision is whether your time to acquire the materials and time/effort to assemble them into a formicarium and/or outworld is worth $230. You would also need to decide how the finished products would compare to what your desired end product is.
I assume you are driving around locally or using public transportation to acquire the materials. You will most likely have to go to multiple locations to acquire all the materials, unless you are lucky enough to have a place that carries all the supplies you will need. If you are having them shipped to you, then you will also be paying shipping and customs fees which would affect this comparison.
You may also need to purchase a few tools to assist in the design/build process. Make sure you factor this into the comparison. Perhaps a drill and/or a few different drill bits for YTong shaping or glass aquarium holes. You may also need to replace a broken YTong block or cracked aquarium if you are inexperienced at shaping YTong or drilling holes through glass aquarium walls. You may laugh at this, but I know of instances where this learning process has resulted in broken YTong or glass aquariums
For some people, their time is more valuable, for others it isn't. For some people, they would rather spend the time to design and build their own, for others they would rather just buy one that someone else has spent the time to design and build. Some people have the skill set to drill holes through glass aquariums, others do not.
I just wanted to provide another viewpoint so that anyone reading this can make a more informed decision.